PSI - Issue 62

Andrea Nettis et al. / Procedia Structural Integrity 62 (2024) 693–700 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

694

2

Nomenclature EDP

engineering demand parameter high-damping rubber bearing

HDRB

IM

intensity measure

LDRB

low-damping rubber bearings

LRB

lead rubber bearings

NLTHA

non-linear time history analysis peak ground acceleration

PGA

1. Introduction and motivation The study of the risk of existing bridges under natural and human-related hazards is a challenging task for transportation management authorities, considering recent collapses leading to relevant financial losses, casualties and extended service downtime periods. The structural safety of bridges and viaducts may be affected by the combination of different hazardous sources, which can be related to natural factors such as earthquakes, floods and hurricanes, or human-induced ones such as traffic, blasts etc.(Anisha et al., 2022; Andrea Nettis et al., 2023; Alessandro Nettis et al., 2023). Several studies proposed by the scientific literature investigate the multi-hazard risk assessment of bridges (Gidaris et al., 2017) dealing with hazard, fragility and consequence models. In addition to the research community, public institutions and transportation managers are working towards the development of procedures for efficient multi-hazard risk assessment. An example is provided by the Italian Guidelines on the safety of existing bridges (Ministero delle Infrastrutture e dei Trasporti, 2020) prescribing a preliminary risk classification of the entire stock of bridges considering traffic and seismic hazards, together with landslides and floods. Considering earthquakes, significant research efforts in the last decades were aimed at proposing seismic fragility models of bridges considering the sole effects of earthquake excitation and analysing the sensitivity of fragility models to different modelling and analysis strategies, bridge structural features and sensitivity to assumptions involved in the fragility assessment process. Recently, multi-hazard risk assessment studies point to extending fragility models adding the consideration of the joint effects of cascading events such as earthquake-triggered landslides or tsunamis and multiple seismic shaking. For example, Mantakas et al. (Mantakas et al., 2023) focus on the seismic response of a case-study simply supported deck single-column bridge in Greece, founded on an active landslide considering the coupling effect of the seismic actions and ground kinematics. Pang et al. (Pang et al., 2022) analyse the fragility of a three-span case-study bridge considering the damage induced by seismic actions together with earthquake-induced landslides. Xu et al. (Xu et al., 2021) analyse the fragility of coastal box-girder bridges under sequential earthquake-tsunami events. Other recent studies investigate seismic fragility considering the combination effect related to additional independent hazard phenomena which can affect the seismic capacity of bridge components. For example, Yilmaz et al. (Yilmaz et al., 2018) study the combination of flood and seismic hazards for an existing bridge in California. Gehl and D’Ayala (Gehl and D’Ayala, 2018) develop a multi-hazard risk assessment procedure based on Bayesian network models to consider the contributions of flood and seismic events on bridge networks. Regarding geohazards, deformations and damages of bridge components can be induced by differential settlements related to soft soil strata (not properly considered in the design) or by low-moving ground movements affecting bridge foundations, typical of areas affected by active landslides. While some recent studies deal with the influence of such phenomena on buildings (Bao et al., 2021; Miano et al., 2022), there is limited information on how differential settlements influence the seismic performance of bridges. On this basis, this paper presents a study on the seismic fragility of continuous-deck bridges isolated through elastomeric bearings subjected to ground settlements. In these cases, the isolation system is placed on substructure components and acts as a flexible layer uncoupling the seismic behaviour of the superstructure from the substructure (Wei et al., 2021). The low stiffness of isolation devices induces large values of vibration periods, inducing significant displacement demand under seismic excitation which is lumped in the isolation layer. In the case of strong seismic actions, the nonlinear response (and hysteretic dissipation) is lumped into the isolation bearings, while